Abstract
The development and improvement of monitoring and process control systems is one of the important ways of advancing laser metal deposition (LMD). The control of hydrodynamic, heat and mass transfer processes in LMD is extremely important, since these processes directly affect the crystallization of the melt and, accordingly, the microstructural properties and the overall quality of the synthesized part. In this article, the data of coaxial video monitoring of the LMD process were used to assess the features of melt dynamics. The obtained images were used to calculate the time dependences of the characteristics of the melt pool (MP) (temperature, width, length and area), which were further processed using the short-time correlation (STC) method. This approach made it possible to reveal local features of the joint behavior of the MP characteristics, and to analyze the nature of the melt dynamics. It was found that the behavior of the melt in the LMD is characterized by the presence of many time periods (patterns), during which it retains a certain ordered character. The features of behavior that are important from the point of view of process control systems design are noted. The approach used for the analysis of melt dynamics based on STC distributions of MP characteristics, as well as the method for determining the moments of pattern termination through the calculation of the correlation power, can be used in processing the results of online LMD diagnostics, as well as in process control systems.
Highlights
∆T = (2700 K − T ) is an inverted value introduced for the convenience of comparing the dynamics of temperature (T) and the size of the melt pool (MP)
During the transition between such periods, the dynamics of the melt loses ordering for a certain time
In different periods, a different structure of movement can be realized. Such behavior of the melt with alternating phases of regular dynamics and moments of reduced ordering can be interpreted as a manifestation of the intermittent behavior of the melt
Summary
Laser metal deposition (LMD) is becoming an important component of modern digital manufacturing. This technology makes it possible to create metal products of complex shapes through the local interaction of concentrated flows of laser energy and powder material. The task of maintaining optimal process parameters that ensure the achievement of the desired physical and mechanical properties of the part is still a serious challenge. This is especially true for parts of complex geometry, including solid and thin-walled or overhanging elements, which predetermines variable heat transfer conditions along the construction path
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